Localization of cracks using vibromodulation detection technique

Abstract

The vibroacoustic modulation technique has been recently introduced as a new tool for nondestructive inspection and evaluation of fatigued, defective, or fractured materials. This technique employs the nonlinear interaction of ultrasound and vibration in the presence of defects. Vibration changes the contact area within a defect effectively modulating an ultrasonic signal passing through this varying contact interface. This paper presents further development of the modulation technique enabling it to determine the location of a defect. The authors have developed and tested various algorithms to find crack location. There are time domain and frequency domain based algorithms. One of the time domain approaches utilizes the correlation between the location of the crack and the arrival time of the modulated portion of the probe ultrasonic signal. This time is determined by the relative distance between locations of the crack and the impact. Another time domain-based approach uses modulation as a ‘‘mark’’ to distinguish the high-frequency tone-burst probe signal reflected from the crack and from all other structural and material inhomogeneities. The frequency domain algorithm analyzes spectral shape which depends on relative position of an impact and a crack. All of these algorithms have been experimentally tested and verified. [Work supported by Gas Research Institute.]